What a good ad agency for a financial information and market data product company to use for digital + print advertising?

There are full-service advertising agencies that would jump at the chance to handle an account matching your description. But they're not going to be big agencies in big cities, typically. Consider small agencies in markets outside of New York, LA, San Francisco, etc. I'm biased because I work at this type of agency (far off the beaten path), but I think you'll get better value and see a lot more interest, in general. I would not recommend hiring a freelancer to handle what's potentially a $240,000/year budget. No doubt you would totally make somebody's day with that kind of assignment. But, in my opinion, you're not likely to get the combination of media and creative expertise that your account will need. You'll also need to be flexible in your expectations, as the budget you specified will not go very far given the publications mentioned. For reference, the WSJ's rate card lists one half-page ad in the national edition (U.S.) at almost $122,000 (gross rate, non-contract). You get good visibility, for sure, but it's probably not the best use of your budget as you'd be spending the majority of your budget to reach a lot of people who have no use whatsoever for your product. A good agency will be able to suggest alternatives that are better targeted to the audience you are trying to reach and more affordable. Look for an agency that's hungry and willing to start small and grow with your company.

At that budget level I don't think you need or can really afford an agency.  You may want to work with a freelancer if you don't feel you have the capability to pull this off. My recommendation would be to meet with some of the sales reps that represent the publishers you mentioned.  Give them a briefing of your objectives and ask them to present an opportunity to you within your budget parameters.  You should be able to evaluate these opportunities internally fairly easily and determine that you can only afford one or two of them anyways.  Given your target audience and publishers you mentioned, I think your best bet is Bloomberg.  They now have advertising within the terminal itself and that's a particularly good bet to reach your audience.